1. Field of the Invention
The present invention relates generally to improved methods of sealing pipe strings in well bores penetrating subterranean corrosive fluid disposal zones.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized as sealants in well completion operations whereby strings of pipe such as casing and liners are sealed in well bores. In performing such operations, a cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
Corrosive waste fluids such as salt water, acidic materials, caustic materials, organic materials, chemical byproduct materials and the like are often disposed of by injecting them into disposal wells. Such disposal wells penetrate subterranean formations which accept large volumes of waste fluids and are naturally separated from other subterranean formations. When a disposal well is completed whereby a string of steel pipe is cemented in the well bore utilizing a hydraulic cement composition, both the set cement and steel pipe are often subjected to severe corrosion. A result of such corrosion in disposal wells can be that the waste fluids leak into and contaminate formations containing useful fluids such as hydrocarbons or potable water.
In order to prevent the corrosion of metal pipe strings in disposal wells, it has heretofore been the practice to seal the pipe strings in the well bores with hardenable epoxy resin sealing compositions. The epoxy resin sealing compositions utilized have been highly resistant to degradation by acids and other corrosive fluids which reduces the corrosion of metal pipe strings and the chances that corrosive fluids will find their way to the surface or into other subterranean locations. However, the hardened epoxy resin sealing compositions have often lacked sufficient resiliency as well as the necessary bond strength to resist loss of pipe and/or formation bond and cracking or shattering as a result of pipe movements caused by expansion, contraction, impacts or shocks. In addition, the epoxy resin sealing compositions utilized heretofore have been intolerant to contact with water. That is, the epoxy resin sealing compositions have contained epoxy resins which are incompatible with water whereby when the compositions are contacted with water, premature hardening of the compositions or other adverse conditions result. Consequently, the epoxy resin sealing compositions have heretofore required the use of oil based pre-flushes and displacement fluids to prevent contact of the compositions with water. The use of such preflushes and displacement fluids is costly and time consuming. Also, even when oil based pre-flushes and displacement fluids are used, water contact with the epoxy resin sealing compositions often takes place causing problems or failures in the sealing operations.
Thus, there are needs for improved methods of sealing pipe strings in disposal wells whereby corrosion resistant, hardenable epoxy sealing compositions are utilized which are compatible with water and also have the resiliencies and high bond strengths required to withstand pipe movements without failure.